Hydraulic continuously variable speed transmission with direct clutch valve

ABSTRACT

A hydraulic continuously variable speed transmission with a direct clutch valve comprises a hydraulic pump, a hydraulic motor, a hydraulic closed circuit for hydraulically connecting the both, a direct clutch valve placed in the closed circuit, a speed reduction ratio control actuator, and a direct clutch valve controlling device for controlling operations of said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially &#34;1&#34;. The direct clutch valve controlling device maintains a direct connecting state when an actual engine speed is higher than a direct clutch disconnecting reference engine speed at the speed reduction ratio of approximately &#34;1&#34;. Then, the direct clutch valve control device releases the blocking of the closed circuit by the direct valve when a drop of the actual engine speed from the direct clutch disconnecting reference engine speed exceeds a predetermined amount corresponding to the vehicle speed.

BACKGROUND OF THE INVENTION

The present invention relates to a hydraulic continuously variable speedtransmission comprising a constant displacement hydraulic pump and avariable displacement hydraulic motor, and more particularly to acontinuously variable speed transmission provided with a direct clutchfor blocking a hydraulic closed circuit, through which the pump ishydraulically connected to the motor, to render the both in a directconnecting state when a speed reduction ratio of the variable speedtransmission has become 1.

Continuously variable speed transmissions have conventionally beenproposed in publications in the Japanese Official Gazette such asJapanese Patent Publication No. 32(1957)-7159, Japanese PatentPublication No. 56(1981)-50142 and the like, wherein a constantdisplacement hydraulic pump is connected to an input shaft, oildelivered from the pump is fed to a variable displacement hydraulicmotor through a closed circuit, and the hydraulic pump is driven todrive an output shaft connected thereto.

It is known to provide a direct clutch which is capable of blocking theabove hydraulic closed circuit, whereby the direct clutch device blocksthe hydraulic closed circuit to integrally rotate the pump and the motorwhen the swash plate angle for variably controlling the displacement ofthe hydraulic motor is minimized (and the speed reduction ratio of thevariable speed transmission becomes 1).

A method for controlling a continuously variable speed transmissionhaving a direct clutch device, as disclosed in Japanese Patent laid-openPublication No. 54(1979)-134252 and Japanese Patent laid-openPublication No. 55(1980)-14312, comprises controlling the speedreduction ratio in such a way that the engine speed coincides with areference engine speed corresponding to the throttle opening to obtainminimum fuel consumption and blocking the closed circuit by the directclutch device to integrally rotate the pump and the motor when the speedreduction ratio becomes minimum or 1.

In controlling the direct clutch, as described above, when the directclutch blocks or opens the closed circuit (when it is switched ON orOFF) at a speed reduction ratio of 1, the load of the engine is changedbecause of change of the hydraulic thrust forces acting on the motorplungers and change of the volumetric efficiency. Therefore thefollowing problems may be produced in the ON/OFF control of the directclutch.

After the direct clutch is switched ON at a speed reduction ratio of"1", a direct clutch disconnecting reference engine speed is setaccording to the engine throttle opening and then the direct clutch isswitched OFF when the actual engine speed becomes smaller than thereference engine speed. When the direct clutch is switched OFF, thehydraulic thrust forces onto the motor plungers are, as described above,restored (increased) and the volumetric efficiency is decreased.Accordingly the engine speed is increased and the actual engine speedbecomes higher than the reference engine speed to switch the directclutch ON causing a "hunting" phenomenon. When tires are locked byaggressive braking in the state of the direct clutch being switched ON(the closed circuit being blocked), the engine may be stalled since ittakes at least some time to relieve the blocking of the closed circuitby the direct clutch valve (i.e., it takes some time to switch thedirect clutch valve OFF).

The reason for engine stall during aggressive braking in a prior arttransmission equipped vehicle is that the vehicle speed is reduced withthe direct clutch valve being switched ON and with the speed reductionratio being minimum. Because the accelerator pedal is released duringaggressive braking to make the throttle opening nearly fully closed,therefore the reference engine speed is lowered according to thethrottle opening. In addition, since the outlet of the hydraulic pump isclosed as long as the direct clutch valve is switched ON, the mainclutch valve, which is used to communicate the outlet of the hydraulicpump with the inlet thereof, is inoperative even if it is opened.Therefore, the problem in the prior art of the engine stall duringaggressive braking cannot be solved.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a continuouslyvariable speed transmission that enables smooth switching of a directclutch valve from ON to OFF without producing a hunting phenomenon.

It is another object of the present invention to provide a continuouslyvariable speed transmission which can be controlled without causingengine stall even when aggressive braking occurs in the ON-state of adirect clutch valve.

In the continuously variable speed transmission according to the presentinvention, once the direct clutch valve is switched on, the directclutch valve controlling device maintains an ON-state of the directclutch valve by blocking a closed circuit as long as an actual enginespeed is higher than a direct clutch disconnecting reference enginespeed set in accordance with a parameter representing a driver'sintention of acceleration, at a speed reduction ratio ofapproximately 1. The blocking of the closed circuit is released when theactual engine speed drops more than a predetermined value from thedirect clutch disconnecting reference engine speed.

In the continuous variable speed transmission described in anotherembodiment of the present invention, the direct clutch valve controllingdevice is adapted to release the blocking of the closed circuit by thedirect clutch valve when a vehicle speed (or an engine speed) detectedby a vehicle (or engine) speed detecting means is lower than apredetermined speed and an accelerator opening detected by anaccelerator opening detecting means is substantially fully-closed duringrunning with the closed circuit blocked by the direct clutch valve.

In this case, the predetermined speed is desirably set higher when thevehicle brakes are applied than when the vehicle brakes are not applied.

The phrase "accelerator opening" used in the specification and claimsmeans an accelerator pedal opening depressed dependent upon the driver'saccelerating intention or an engine throttle valve opening responsive tothe depression of accelerator pedal. The accelerator opening is fullyclosed when the accelerator pedal is completely released and fullyopened when it is completely depressed.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by may of illustration only, and thus are not limitativeof the present invention and wherein:

FIG. 1 is a hydraulic circuit diagram of a continuously variable speedtransmission having a direct clutch device according to the presentinvention;

FIG. 2 is cross-sectional view of the continuously variable speedtransmission;

FIG. 3 shows cross-sectional views of first and second servo units usedin the continuously variable speed transmission;

FIG. 4 is a cross-sectional view of the direct clutch device;

FIG. 5 is a perspective view showing a link mechanism;

FIGS. 6B to 6C are front views showing the actuation of a cam composingthe link mechanism;

FIG. 7 is a graph showing the traveling characteristics of a vehiclewith the continuously variable speed transmission according to a firstembodiment;

FIG. 8 is a flowchart showing the OFF-control of the direct clutch valveaccording to the first embodiment;

FIG. 9 is a graph showing a relationship between the vehicle speed andthe engine speed difference dNe for the above OFF-control;

FIG. 10 is a graph showing the traveling characteristics of a vehiclewith the continuously variable transmission according to a secondembodiment; and

FIG. 11 is a flowchart showing the OFF-control of the direct clutchvalve according to the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A hydraulic circuit diagram of a continuously variable speedtransmission with a direct clutch unit in accordance with the presentinvention is presented in FIG. 1 wherein the continuously variable speedtransmission T has a constant displacement swash plate type axialplunger hydraulic pump P driven by an engine E through an input shaft 1and a variable displacement swash plate type axial plunger hydraulicmotor M which drives wheels W through a directional change unit 20. Thepump P and the motor M are connected with each other by means of twohydraulic lines La and Lb composing a closed hydraulic circuit whereinthe first line La connects the pump outlet port to the motor inlet portand the second line Lb connects the pump inlet port to the motor outletport. The internal pressure of the first line La is high when the engineE drives the wheels W through the pump P and the motor M (the internalpressure of the second line Lb is low at this time). On the other hand,the internal pressure of the second line Lb is high when the engine E isdriven by the wheels W creating engine braking phenomenon (the internalpressure of the first line La is low at this time). The engine brakingphenomenon occurs during a deceleration state of the vehicle, forexample.

Further, a direct clutch valve DC which can block the first line La isplaced in the first line La.

An outlet port of a charge pump 10 which is driven by the engine E isconnected to the closed hydraulic circuit through a charge line Lhhaving a check valve 11 and a third line Lc having a pair of checkvalves 3, 3. The oil pumped up from an oil sump 15 by the charge pump 10and regulated in pressure by a charge pressure relief valve 12 is fed tothe one of the two lines La and Lf which has lower hydraulic pressure init by means of the check valves 3, 3. A fourth line Ld having a shuttlevalve 4 is also connected to the closed hydraulic circuit. The shuttlevalve 4 is connected to the oil sump 15 through a fifth line Le and asixth line, Lf having a high pressure relief valve 6 and a low pressurerelief valve 7, respectively. The shuttle valve 4 is a 2-port 3-positiontype control valve and is functioned by the difference of the pressuresinside the first and the second lines La and Lb. Therefore, either ofthe two lines La and Lb which has higher pressure is connected to thefifth line Le and the oil pressure in it is regulated by the highpressure relief valve 6. The other of the two lines and Lb which haslower pressure is connected to the sixth line Lf and the oil pressure init is regulated by the low pressure relief valve 7.

In a seventh line Lg, through which the first line La is connected tothe second line Lb, is placed a main clutch valve CL made of a variablethrottle valve which controls the opening of the seventh line Lg.

An output shaft 28 connected to the wheels W is placed in parallel withthe drive shaft 2 of the hydraulic motor M. A directional change gearunit 20 is placed between these two shafts 2 and 28. This gear unit 20comprises a first drive gear 21 and a second drive gear 22 firmlymounted on the drive shaft 2 leaving an axial space therebetween, afirst driven gear 23 rotatably mounted on the output shaft 28 andengaged with the first drive gear 21, a second driven gear 25 rotatablymounted on the output shaft 28 and engaged with a intermediate gear 24which is engaged with the second drive gear 22, a clutch hub 26 placedbetween the first and second driven gears 23, 25 and firmly mounted onthe output shaft 28, and a sleeve 27 slidably mounted on the clutch hub25 which can be selectively engaged with clutch gears 23a, 25a formed onthe sides of the driven gears 23, 25. The sleeve 27 can be movedlaterally by a shift fork 29. In the directional change gear unit 20,when the sleeve 27 is slid leftward by the shift fork 29, the clutchgear 23a of the first driven gear 23 is connected to the clutch hub 26by means of the sleeve 27 (as shown in FIG. 1). Hence the rotationaldirection of the output shaft 28 is opposite to that of the drive shaft2 and the wheels W are driven forward by the continuously variable speedtransmission T. On the other hand, when the sleeve 27 is slid rightwardby the shift fork 29, the clutch gear 25a of the second driven gear 26is connected to the clutch hub 25 by means of the sleeve 27. Hence, therotational direction of the output shaft 28 is the same as that of thedrive shaft 2 and the wheels W are driven rearward.

Actuators which control the variable displacement of the hydraulic motorM to adjust the speed reduction ratio of the transmission are a firstand a second servo unit 30, 50 which are connected by a link mechanism40 with each other. These units 30, 50 are also used to control theoperation of the direct clutch valve DC.

The operations of the servo units 30, 50 are controlled by a pair ofsolenoid valves 151, 152 which are actuated by duty cycle signals from acontroller 100. Signals correspondig to vehicle speed V (sent through aline 100a), engine speed Ne (sent through a line 100b), engine throttleopening degree θth (sent through a line 100c), swash plate angle θtr ofthe hydraulic motor M, manual shift lever position Psl, brake actuationBR (sent through a line 100d) and opening degree θcl of the directclutch valve DC are inputted into the controller 100. Based on theseinput signals, the controller 100 outputs duty cycle signals to theabove solenoid valves to effectuate desirable traveling control.

A sectional view of the continuously variable speed transmission T ispresented in FIG. 2 wherein the transmission T includes the hydraulicpump P and the hydraulic motor M which are coaxially placed in a spacesurrounded by cases 5a, 5b and a cover 5c.

The hydraulic pump P comprises a pump cylinder 60 splinejointed with theinput shaft 1, a plurality of cylinder holes 61 being formed in the pumpcylinder 60 equally spaced along the circumferential plane, and aplurality of pump plungers 62 inserted into the cylinder holes 61. Thepump P is driven by the engine E through a flywheel Fw to which theinput shaft 1 is connected.

The hydraulic motor M comprises a motor cylinder 70 which encircles thepump cylinder 60, a plurality of cylinder holes 71 being formed in themotor cylinder 70 equally spaced along the circumferential plane whichcoaxially encircles the pump cylinder 60, and a plurality of motorplungers 72 inserted in the cylinder holes 71. The hydraulic motor M canbe relatively rotated on the axis of the pump cylinder.

The motor cylinder 70 has a pair of support shafts 78a, 78b at bothends. These support shafts 78a, 78b are rotatably sustained by the case5a, 5b with a needle bearing 79a and a ball bearing 79b. The supportshaft 78a is the same thing as the output shaft 2. The first and thesecond drive gears 21, 22 of the directional change gear unit 20 aremounted on the support shaft 78a (the output shaft 2) by means of aspline-joint.

On the left inside surface of the motor cylinder 70 is firmly mounted apump swash plate 63 being inclined at a predetermined angle. An annularpump shoe 64 is slidably mounted on the pump swash plate 63. The pumpplungers 62 are swingably connected to the pump shoe 64 by means ofconnecting rods 65 which have ball joints at both ends.

The annular pump shoe 64 is rotatably supported by the motor cylinder 70with a needle bearing 66 placed along the periphery of the pump shoe 64.The pump shoe 64 is pushed against the pump swash plate 63 by a spring67c through a retaining ring 67a and a spring support 67b which havespherical contact surfaces. Accordingly the pump shoe 64 can be rotatedon the pump swash plate 63.

Two bevel gears 68a, 68b having the same number of teeth and engagingwith each other are fixed on the pump shoe 64 and the pump cylinder 60respectively. When the pump cylinder 60 is driven by the engine Ethrough the input shaft 1, the pump shoe 64 is also driven by means ofthe two bevel gears 68a, 68b. While the pump cylinder and the pump shoeare rotated, the pump plungers 62 which run on the ascending side of theinclined pump swash plate 63 are contracted (intake condition) and thepump plungers 62 which runs on the descending side of the pump swashplate 63 are expanded (exhaust condition).

A motor trunnion plate 73 which is opposite the motor plungers 72 isplaced inside the cases 5a, 5b and supported swingably by the cases 5a,5b around the trunnion axis 73a which is perpendicular to the surface ofthe drawing (FIG. 2). Motor shoes 74 are slidably placed on the swashplate 73b of the trunnion plate 73 and swingably connected to the balljoint portions 72a formed at the ends of the motor plungers 72.

According to reciprocating motions of the motor plungers 72, the motorcylinder 70 is rotated. When the tilt angle of the motor trunnion plate73 is varied as discussed below, the strokes of the motor plungers 72are varied from 0 to maximum. The strokes are 0 when the motor trunnionplate 73 is perpendicular to the axes of the motor plungers 72 and aremaximum when the tilt angle is maximum as shown in FIG. 2.

The motor cylinder 70 consists of a first, a second, a third and afourth section 70a, 70b, 70c, and 70d, respectively. The support shaft78a is formed on the first section 70a and the pump swash plate 63 isplaced inside the first section 70a. The cylinder holes 71 in which themotor plungers 72 are inserted are formed in the second section 70b. Adistribution plate 80 having hydraulic lines which communicate with thecylinder holes 61, 71 is formed in the third section 70c. The supportshaft 78b is formed in the fourth section 70d. These sections 70a, 70b,70c, 70d are positioned by fits and pins and joined together by bolts77a, 77b.

The pump cylinder 60 is pushed against the third section 70c (thedistribution plate 80) by the biasing force of the spring 67c to preventoil leakage from the contact surfaces.

In the fourth section 70d having the support shaft 78b is formed ahollow space where a fixed shaft 91 is inserted. A distribution ring 92which is in contact with the distribution plate 80 is eccentricallymounted at the left end of the fixed shaft 91. The hollow space in thefourth section 70d is divided into two chambers defining an innerchamber and an outer chamber, the inner chambers being a part of thefirst line La and the outer chamber being a part of the second line Lb.

A pump exhaust port 81a and a pump intake port 82a are formed in thedistribution plate 80. The cylinder holes 61 of the pump plungers 62which are in the exhaust condition communicate with the first line Lathrough the exhaust port 81a and the exhaust line 81b connected thereto.Also, the cylinder holes of the pump plungers 62 which are in the intakecondition communicate with the second line Lb through the intake port82a and the intake line 82b connected thereto. Further, a first line(not shown) and a second line 83 are formed in the distribution plate80. The cylinder holes 71 of the motor plungers 72 which are in theexpansion condition communicate with the first line La through the firstline. The cylinder holes 71 of the motor plungers 72 which are at thecontraction condition communicate with the second line Lb through thesecond line 83.

Accordingly, the hydraulic pump P and the hydraulic motor M areconnected with each other by the closed hydraulic circuit which isformed in the distribution plate 80 with the use of the distributionring 92. When the pump cylinder is driven by the engine E through theinput shaft 1, the pressurized oil exhausted by the pump plungers 62 isfed to the cylinder holes 71 of the motor plungers 72 which are in theexpansion condition through the exhaust port 81a, the exhaust line 81b,the first line La and the first line (not shown). Also, the oilexhausted by the motor plungers which are in the contraction conditionis fed to the cylinder holes 61 of the pump plungers 62 which are in theintake condition through the second line 83, the second line Lb, theintake line 82b and the intake port 82a. The reaction torque applied tothe motor cylinder 70 by the pump plungers 62 which are in the exhaustcondition and the reaction torque applied to the motor plungers 72 whichare in the expansion condition drive the motor cylinder 70.

Speed reduction ratio can be calculated according to the followingequations:

    ______________________________________                                        S.R. Ratio =                                                                           (speed of pump cylinder 60)/(speed of motor                                   cylinder 70)                                                         =        1 + (displacement of motor M)/(displacement of                                pump P)                                                              ______________________________________                                    

Thus, if the displacement of the hydraulic motor M is varied, the speedreduction ratio (S.R. Ratio) can be varied from 1 (minimum) to maximum.

Displacement of the hydraulic motor M is determined in accordance withthe stroke of motor plungers 72. Therefore, the speed reduction ratiocan be varied steplessly by controlling tilt angle of the trunnion plate73.

Tilt angle of the trunnion plate 73 is controlled by the first andsecond servo units 30, 50. The first servo unit 30 is placed on theupper portion of the case 5b. The first servo unit 30 is connected tothe second servo unit 50 through the link mechanism 40. These valves 30,50 are shown in FIG. 3 and the constructions and operations thereof aredescribed hereinafter.

The first servo unit 30 comprises a housing 31 having a connection port31a connected to the high pressure line 120, a piston member 32 slidablyinserted into the housing 31, and a spool member 34 slidably andcoaxially inserted into the piston member 32. High pressure oil in theclosed hydraulic circuit of the transmission T is fed to the highpressure line 120 through the shuttle valve 4 and the fifth line Le. Thepiston member 32 consists of a piston portion 32a formed at its rightend and a rod portion 32b coaxially extending leftward therefrom. Thepiston portion 32a is inserted into a cylinder hole 31c of the housing31 and divides the space inside the cylinder hole 31c into two chambersdefining two cylinder rooms 35, 36. The rod portion 32b, having asmaller diameter than the cylinder hole 31c, is inserted into a rod hole31d which is concentric with the cylinder hole 31c. The right cylinderchamber 36 is covered by a plug member 33a and a cover 33b through whichthe right end of the spool member 34 protrudes.

The high pressure line 120 connected to the port 31a communicates withthe left cylinder chamber 35 through a hydraulic line 31b. The pistonmember 32 is pushed rightward by the hydraulic pressure fed in the leftcylinder chambers 35 through the high pressure line 120.

A land portion 34a which is inserted in a spool hole 32d is formed atthe left end of the spool member 34. A pair of dents 34b having diagonalplanes with fixed axial widths is formed at the right side of the landportion 34a. A stop ring 37 mounted on the spool member 34 hits againsta stop ring 38 mounted on the inside surface of the piston member 32before the spool member 34 comes out.

A drain passage 32e which can connects the right cylinder chamber 36 tothe oil sump (not shown) through the spool hole 32d responding to therightward motion of the spool member 34 and a connection passage 32cwhich can connect the left cylinder chamber 35 to the right cylinderroom 36 through the dents 34b responding to the leftward motion of thespool member 34 are formed in the piston member 32.

When the spool member 34 is moved rightward, the land portion 34a blocksthe connection passage 32c and opens the drain passage 32e. Accordinglythe hydraulic pressure fed through the high pressure line 120 is led inthe left cylinder chamber 35 and pushes the piston member 32 rightwardso that the piston member 32 follows the spool member 34. When the spoolmember 34 is moved leftward, the connection passage 32c communicateswith the right cylinder chamber 36 through the dents 34b and the drainpassage 32e is blocked by the land portion 34a. Accordingly the highhydraulic pressure is fed to both the left and right cylinder chambers35, 36. The piston member 32 is pushed leftward because of thedifference in areas where pressure is applied and therefore the pistonmember 32 is moved so as to follow the spool member 34.

When the spool member 34 is held still, the piston member 32 is alsoheld still creating a hydraulic floating state because of pressure abalance between the left and right cylinder chambers 35, 36.

As discussed, when the spool member 34 is moved leftward or rightward,the piston member 32 is moved laterally so as to follow the spool member34 with the help of the high hydraulic pressure fed through the highpressure line 120. Accordingly the variable displacement of the motor Mis controlled by the motion of the spool member 34 since the pistonmember 32 is connected to the swash plate 73 of the motor M by means ofa link member 39.

The spool member 34 is linked to the second servo unit 50 by means of alink mechanism 40. The link mechanism 40 includes a first link member 42being swingable around an axis 42c and having two arms 42a and 42bperpendicular to each other, and a second link member 48 pivotallyconnected to the arm 42b. The upper end of the arm 42a is pivotallyconnected to the right end of the spool member 34. The bottom end of thesecond link member 48 is pivotally connected to a spool member 54 of thesecond servo unit 50. Therefore when the spool member 54 of the secondservo unit 50 is moved up or down, the spool member 34 of the firstservo unit 30 is moved rightward or leftward.

The second servo unit 50 comprises a housing 51 having ports 51a, 51b towhich hydraulic lines 102, 104 are connected respectively, and the spoolmember 54 vertically slidably fitted in the housing 51. The spool member54 consists of a piston portion 54a and a end spool portion 54bcoaxially extending downward therefrom. The piston portion 54a isinserted into a cylinder hole 51c of the housing 51 and divides thechamber inside the cylinder hole 51c covered by a cover 55 into twochambers defining an upper and a lower cylinder chamber 52 and 53,respectively. The end spool portion 54b is fitted into a rod hole 51dwhich is concentric with the cylinder hole 51c and extends downward.

A spool 58a of a top position detecting switch 58 is projected into arecess 54e formed on the end spool portion 54b. The spool 58a is pushedup along the tapered surface of the recess 54e when the spool member 54is moved up. Therefore it can be found by the top position detectingswitch 58a if the speed reduction ratio has become minimum or not, sincethe pushed-up spool 58a turns the switch 58 on.

Further, the hydraulic lines 102, 104 communicate with the upper andlower cylinder chambers 52, 53 through the ports 51a, 51b. The spoolmember 54 is moved up or down by the difference of hydraulic forcesapplied to the piston portion 54a which are determined based on thedifferences of hydraulic pressures and of the areas where the hydraulicpressures in the cylinder chambers 52, 53 are applied. The up and downmotions of the spool member 54 are transmitted to the spool member 34 ofthe first servo unit 30 by the link mechanism 40 causing right and leftmotions of the spool member 34. In other words, the control of thehydraulic pressures supplied through the hydraulic lines 102, 104enables control of the motion of the spool member 34 and the pistonmember 32 in the first servo unit 30 and also enables control of theswash plate angle of the hydraulic motor M and the displacement thereof.In fact, when the spool member 54 of the second servo unit 50 is movedup, the piston member 32 of the first servo unit 30 is moved rightwardlessening the swash plate angle, the displacement of the hydraulic motorM and the speed reduction ratio.

As shown in FIG. 1, hydraulic oil whose pressure is regulated by thecharge pressure relief valve 12 is led to the hydraulic line 102 througha hydraulic line 101. Hydraulic oil in the hydraulic line 102 is led tothe hydraulic line 104 through a hydraulic line 103 having an orifice103a, and the hydraulic pressure in the hydraulic line 104 is controlledby the two solenoid valves 151, 152 which are operated based on dutycycle signals from the controller 100. Accordingly it is said that thesignals from the controller 100 control the operations of the first andsecond servo units 30, 50 and consequently adjust the displacement ofthe hydraulic motor M.

Referring now to the main clutch CL and the direct clutch DC shown inFIG. 4: The main clutch CL and the direct clutch DC are disposed insidethe fixed shaft 91 which is inserted in the hollow space formed in thefourth section 70d of the motor cylinder 70.

A cylindrical bearing member 93 is mounted on the outside surface of thefixed shaft 91. The motor cylinder 70 is rotatably supported by thefixed shaft 91 with the bearing member 93.

Shortcut ports 91a, 91b through which the first line La can communicatewith the second line Lb are bored through the circumferential wall ofthe fixed shaft 91. In the inner cylindrical space of the fixed shaft 91is inserted a main clutch valve body 95 by which the shortcut ports 91a,91b are opened or closed.

The main clutch valve body 95 is rotatably supported by the fixed shaft91 with a radial needle bearing 96a and a thrust needle bearing 96b.Shortcut holes 95a, 95b which can be mated with the shortcut ports 91a,91b are bored through the valve body 95. A rotator arm 97 is integrallyconnected to the right end of the valve body 95. In accordance with therotation of the main clutch valve body 95 by the rotator arm 97, theshortcut holes 95a, 95b can be mated with the shortcut ports 91a, 91b.Accordingly, when the shortcut holes 95a, 95b are mated throughly withthe shortcut ports 91a, 91b, the main clutch CL becomes OFF(disconnected) state. When the shortcut holes 95a, 95b are partiallymated with the shortcut ports 91a, 91b, the main clutch CL becomessemi-ON (partially connected) state. When the shortcut holes 95a, 95bare in discord with the shortcut ports 91a, 91 b, the main clutch CLbecomes ON (connected) state. When the main clutch is in the OFF state,the oil fed in the first line La from the outlet port 81a of the pump issent directly in the inlet port 82a of the pump through the shortcutports 91a, 91b and the second line Lb. Therefore, the motor M isinoperative in spite of the operation of the pump P. When the mainclutch CL is in the ON state, the oil is circulated in the closedhydraulic circuit and the power is transmitted from the pump P to themotor M. A means to rotate the rotator arm 97 for the ON-OFF actions ofthe main clutch CL is not described here since it is wellknown.

The direct clutch DC is disposed inside the main clutch valve body 95. Apiston shaft 85 is slidably inserted in the cylindrical hole of thevalve body 95. A valve rod 86a is screwed in the end of the piston shaft85. A valve shoe 86b is swingably connected to the end of the valve rod86a by means of a spherical joint.

When the piston shaft 85 is moved leftward, the left end of the valveshoe 86b comes in contact with the distribution plate 80 and closes theoutlet port 81b of the pump P. While the exhaust port 81b is closed, thepump plungers 62 are hydraulically locked and the pump P is directlycoupled with the motor M. Accordingly the motor cylinder 70 ismechanically driven by the pump cylinder 60 through the pump plungers 62and the pump swash plate 63. The direct coupling of the pump P and themotor M is executed at the upright (top) position of the motor trunnionplate 73, wherein the speed reduction ratio is minimum. When the pump Pand the motor M are directly coupled, the thrust force applied on themotor trunnion plate 73 by the motor plungers 72 and the frictionbetween the swash plate 73b and the motor shoes 74 are decreased andconsequently loads applied on each member such as bearings are lessened.

A hydraulic chamber 87a is formed between the right portion of thepiston shaft 85 and the inner member 96c of the thrust needle bearing96b which supports the valve body 95. The hydraulic chamber 87a normallycommunicates with the first line La through a line 89a and a line 89b,the line 89a being drilled in parallel with the axis of the piston shaft85 and the line 89b being drilled through along the axis of the valverod 86a so as to connect the line 89a to the first line La. Duringoperation, the high pressure oil in the closed hydraulic circuit isalways fed to the hydraulic chamber 87a.

The piston shaft 85 has a piston portion 85a in the middle thereof. Acircular hydraulic chamber 87b is formed on the left side of the pistonshaft 85 between the inner surface of the main clutch valve body 95 andthe outer surface of the piston shaft 85. A center hole 88 extendingalong the central axis is formed on the right end of the piston shaft 85and an escape groove 88a is formed on the bottom of the center hole 88.The center hole 88 can communicate with the circular hydraulic chamber87b through a communicating hole 89c. The line 89a communicates with thecenter hole 88 through a communicating hole 89d.

A rod-shaped pilot valve 84 is inserted in the center hole 88. A landportion 84a which is fitted in the center hole 88 is formed on the endof the pilot valve 84. A groove portion 84b adjacent to the land portion84a is also formed on the pilot valve 84. By a communicating hole 89eformed in the pilot valve 84, the center hole 88 communicates with theatmosphere. The pilot valve 84 is laterally moved by a link arm 46 (FIG.5) connected thereto. The action of the link arm 46 is described later.

In the above construction of the direct clutch DC, the following areas,

the pressure applied area of the shoe 86b: A

the sectional area of the piston portion 85a: B

the pressure applied area of the left part of the piston shaft 85: C

the sectional area of the right part of the piston shaft 85: D

are decided so as to satisfy the following inequalities.

    A>(B-D)

    (B-D)>C

When the pilot valve 84 is moved leftward, the communicating hole 89d isclosed by the outer surface of the pilot valve 84. Accordingly the highpressure oil fed from the exhaust port 81a is directed to the hydraulicchamber 87a through the lines 89a, 89b and its hydraulic pressure isapplied on the right side surface of the piston portion 85a. Thishydraulic pressure is also applied on the left part of the piston shaft85. Since the pressure applied area of the right side surface of thepiston portion 85a is (B-D) and the pressure applied area of the leftpart of the piston shaft 85 is C, the piston shaft 85 is moved leftwardin accordance with the inequality (B-D)>C. When the piston shaft 85 ismoved leftward, the shoe 86b comes in contact with the distributionplate 80 and closes the exhaust line 81b causing a direct connectingstate of the pump P and the motor M.

At this direct connecting state, the high pressure oil (whose pressureis the same as that in the hydraulic chamber 87a) from the exhaustingport 81a is applied on the end surface of the shoe 86b having a pressureapplied area of A. The high pressure oil in the hydraulic room 87a isapplied on the left surface of the piston portion 85a having a pressureapplied area of (B-D). Accordingly, the shoe 86b is pushed rightward inaccordance with the inequality A>(B-D). However, if the shoe 86 is movedrightward even slightly, the shoe is moved back immediately, because thehydraulic force applied on the end surface of the shoe 86b is releasedas soon as the shoe 86b is moved rightward.

Therefore, the shoe 86b is kept in a so-called hydraulic floating state,and the leakage through a clearance between the shoe 86a and the exhaustline 81b is minimized.

When the pilot valve 84 is move rightward, the groove portion 84b of thepilot valve 84 communicates with the communicating hole 89d. Thereforethe high pressure oil is applied not only on the right side surface ofthe piston portion 85a and the left part of the piston shaft 85 but onthe left side surface of the piston portion 85a since the oil is fed tothe chamber 87b through the hole 89d, the groove portion 84b and theline 89c. Since the pressure applied area for giving leftward force tothe piston shaft 85 is (B-D) and that for giving rightward force to itis B, the piston shaft is moved rightward in accordance with aninequality B>(B-D). Consequently, the direct connection of the pump Pand the motor M is canceled. Thus, the ON-OFF actions of the directclutch DC are controlled by the lateral movement of the piston shaft 85which follows the pilot valve 84.

The lateral movement of the pilot valve 84 is controlled by the secondservo unit 50 which is connected to the pilot valve 84 through the linkmechanism 40. The construction and the action of the link mechanism 40are described hereinafter.

As illustrated in FIG. 5, the link mechanism 40 includes a first shaft42c having two arms 42a, 42b and a second shaft 45 placed under and inparallel with the first shaft 42c, the both shafts 42c, 45 beingrotatably supported by the bearings 49a, 49b and 49c. The first and thesecond servo units 30, 50 are linked by means of the link arms 42a, 42b,the arm 42a being connected to the spool member 34 of the first servounit 30 and the arm 42b being connected to the spool member 54 of thesecond servo unit 50 through the second link member 48.

The link arm 46 which is connected to the pilot valve 84 of the directclutch DC is firmly mounted on the second shaft 45. When the link arm 46is swung corresponding to the rotation of the second shaft 45, the linkarm 46 moves the pilot valve 84 laterally. Consequently the ON-OFFaction of the direct clutch DC is controlled by the pilot valve 84. Thelink arm 46 is always being pushed by a torsion coil spring 46a mountedon the second shaft 45 so as to pull the pilot valve 84 out.

A drive cam 43 and a driven cam 44 which are in contact, with eachother, are fixed on the first and the second shafts 42c 45 respectively.By the actions of these cams 43, 44, the second shaft 45 is rotated asthe first shaft is rotated.

The actions of the cams 43, 44 are described here referring FIGS. 6A-6C.As shown in these drawings, the drive cam 43 comprises a semicircularportion 43a which is concentric with the first shaft 42c, a convexportion 43b which projects out of the periphery of the semicircularportion 43a and a concave portion 43c which is indented below theperiphery of the semicircular portion 43a. The driven cam 44 comprisesan concaved arc portion 44a having almost the same curvature as that ofthe semicircular portion 43a and a linear portion 44b extending alongthe tangential line of the arc portion 44a.

When the spool member 54 of the second servo unit 50 is at a bottomposition and the inclination angle of the trunnion plate 73 of the motorM is maximum (the speed reduction ratio is also maximum), thesemicircular portion 43a of the drive cam 43 is in contact with theconcaved arc portion 44a of the driven cam 44 and the convex portion 43bis apart from the linear portion 44b as shown in FIG. 6A. Accordingly,the pilot valve 84 is moved right by the force of the torsion coilspring 46a transmitted through the link arm 46 and the direct clutch DCis fully opened.

Then, when the spool member 54 is moved up to decrease the inclinationangle of the trunnion plate 73, the first shaft 42c is rotated clockwiseand therefore the trunnion plate 73 is also rotated clockwise around thetrunnion axis 73a by the first servo unit 30. Consequently theinclination angle of the trunnion plate 73 and the speed reduction ratioare decreased. At this time, the drive cam 43 is rotated as the firstshaft 42c is rotated. However, the driven cam 44 is not rotated untilthe convex portion 43b comes in contact with the linear portion 44b.Therefore the pilot valve 84 remains still and the direct clutch DC iskept open.

When the spool member 54 of the second servo unit 50 is further moved upuntil the speed reduction ratio becomes "1" (minimum) (the motortrunnion plate being perpendicular to the motor axis), the convexportion 43b of the drive cam 43 which has been rotated clockwise withthe first shaft 42c comes in contact with the linear portion 44b of thedriven cam 44 as shown in FIG. 6B. It can be found by a top positiondetecting switch 58 that the motor trunnion plate 73 has becomeperpendicular to the motor axis and the speed reduction ratio has become"1".

When the spool member 54 is further moved up, the first shaft 42c isfurther rotated clockwise. The spool member 34 of the first servo unit30 is pushed rightward, but the motor trunnion plate 73 is kept still,already being perpendicular to the motor axis. In the mean time, sincethe drive cam 43 is rotated clockwise with the first shaft 42c, thelinear portion 44b is pushed by the convex portion 43b as shown in FIG.6c and consequently the driven cam 44 is rotated clockwise.

The second shaft 45 and the link arm 46 are also rotated clockwise inaccordance with the rotation of the driven cam 44 against the torsioncoil spring 46a. Accordingly the pilot valve 84 is pushed leftward. Thenthe piston shaft 85 is also moved leftward and the direct connectingstate (the ON-state of the direct clutch valve DC) is created since theshoe 86b blocks the exhaust line 81b.

Then, if the spool member 54 of the second servo unit 50 is moveddownward, it performs actuation reverse to the above-described actuationwhereby the inclination angle of the motor trunnion plate 73 isincreased to increase the speed reduction ratio after a direct clutchvalve has been switched OFF.

Methods for controlling the operation of the main clutch valve CL andthe direct clutch valve DC and for controlling the inclination of themotor trunnion plate 73 of the continuously variable speed transmissionin the above structured are described below.

FIG. 7 is a graph showing a relationship between the engine speed andthe vehicle speed in a vehicle on which the continuously variable speedtransmission is mounted. In the graph, straight lines P and Q shows thecharacteristics at the maximum and minimum speed reduction ratiosrespectively. When the vehicle speed is zero and the engine is in anidling state, the main clutch CL is OFF with the speed reduction ratiobeing maximum and the direct clutch DC is also OFF. When an acceleratorpedal is depressed to increase the throttle opening thereby increasingthe engine speed, the vehicle speed is increased controlling the speedreduction ratio so that the engine speed coincides with the referenceengine speed corresponding to the accelerator opening. In the control,for instance, the vehicle speed varies in the order of L₁ (engagement ofthe main clutch) to L₂ (increase of the vehicle speed with increase ofthe engine speed at the maximum speed reduction ratio) to L₃ (increaseof the vehicle speed by decreasing the speed reduction ratio whilekeeping the engine speed constant) to L₄ and L₈ (increase of the vehiclespeed with increase of the engine speed at the minimum speed reductionratio). At a transition point from the state L₃ to the state L₄ (point"a"), the direct clutch valve DC is switched from OFF to ON. Thetraveling characteristics along the lines L₁ to L₄ shown herein varieswith the degree of depression of the accelerator pedal. For example,when the depression of the accelerator pedal is great and fast,connection control of the main clutch and speed reduction control of thetransmission are conducted at a high engine speed, for example, alongthe lines L₅, L₆, L₇ and L₈ in the graph.

A flowchart in FIG. 8 explains a method of controlling the direct clutchvalve DC to switch OFF after it is switched ON. In the control, a directclutch disconnecting reference engine speed (for example, the enginespeed shown in the chain line R in FIG. 7) corresponding to theaccelerator opening (the opening of the engine throttle or that of theaccelerator pedal) is set. Then the actual engine speed is read-in todetermine whether the direct clutch valve is being switched ON or OFF.When the direct clutch valve DC is yet being switched OFF, the normalspeed reduction control is performed so that the actual engine speedcoincides with the reference engine speed according to the acceleratoropening.

When the clutch valve DC is being switched ON, the actual engine speedis compared with the direct clutch disconnecting reference engine speed.If the actual engine speed is higher than the reference engine speed,the direct clutch valve DC is kept being switched ON. If the later ishigher than the former, a decision is made whether or not absolute valuedNe of the difference between the actual engine speed and the referenceengine speed is larger than the predetermined speed difference DN. Thepredetermined speed difference DN corresponds, as shown in FIG. 9, tothe speed difference previously set against the vehicle speed (forexample, the predetermined speed difference dNe for 100 km/H of thevehicle speed is 100 rpm with reference to the graph). The predeterminedspeed difference DN is set in view of the fact that the increment ofengine speed when the direct clutch valve DC is switched from OFF to ONvaries nearly corresponding to the vehicle speed. Also, the differenceDN is set somewhat larger than the increment of the engine speed at eachvehicle speed in the case of ON-OFF switching of the direct clutchvalve.

The direct clutch valve DC is kept switched ON when the absolute valuedNe of the difference between the reference engine speed and the actualengine speed is smaller than the predetermined engine speed differenceDN (in the ON region in FIG. 9), whereas the direct clutch valve DC isswitched OFF when the difference between the reference engine speed andthe actual engine speed is larger than the predetermined engine speeddifference DN (in the shaded OFF region in FIG. 9). In other words, thedirect clutch DC is switched from ON to OFF when the engine speed isdecreased along the straight line Q (L₄ and L₈) in FIG. 7, to a speedcorresponding to the point d at which the line Q crosses the line S. Atthe point d, the engine speed is lower than the reference engine speed Rby the predetermined speed difference DN.

In this case, the control is so conducted that the engine speedcoincides with the reference engine speed. The direct clutch is switchedfrom OFF to ON when the speed reduction ratio has become "1". Then it isswitched from ON to OFF when a drop of the actual engine speed from thedirect clutch disconnecting reference engine speed is bigger than thepredetermined speed difference DN corresponding to the vehicle speed.The predetermined speed difference DN corresponds to the increment ofthe engine speed produced at the switching of the direct clutch from ONto OFF and the increment is set corresponding to the vehicle speedbecause it nearly varies with the vehicle speed. Therefore, theincreased engine speed never exceeds the reference engine speed and nohunting phenomenon is produced even if the engine speed is increased atthe switching of the direct clutch from ON to OFF.

A control of ON-OFF switching of the direct clutch valve DC inaccordance with the accelerator opening is described above. Next, acontrol method of switching the direct clutch valve DC from ON to OFFwhen the accelerator opening is closed is described below with referenceto the flowchart in FIG. 11 as a second embodiment. In this control, thereference engine speed is set according to the accelerator opening andthen the actual engine speed is read. Then it is decided whether thedirect clutch valve DC is being switched ON or OFF. When the directclutch valve is being switched OFF, a normal speed reduction control isconducted such that the actual engine speed is in agreement with thereference engine speed corresponding to the accelerator opening.

On the other hand, when the direct clutch valve DC is switched ON, it isdetected whether or not the accelerator opening is zero (whether or notthe accelerator pedal is depressed) based on an accelerator openingsignal θacc. When the depression of the accelerator pedal is detected,the control as shown in FIG. 8 is conducted. Namely, the ON/OFFoperation of the direct clutch valve DC is controlled based on thedirect clutch disconnecting reference engine speed which is setaccording to the accelerator opening.

If the accelerator opening is zero, whether or not the vehicle brake isactuated is then decided. If the vehicle speed is reduced withoutactuation of the brakes, it is decided whether or not the actual vehiclespeed is lower than a first predetermined vehicle speed V₁ set forunactuated braking. The direct clutch valve DC is kept being switched ONwhen the actual vehicle speed is higher than the first predeterminedvehicle speed V₁ and is switched OFF when the actual vehicle speed islower than the first predetermined vehicle speed V₁. On the other hand,when the brakes are applied to reduce the vehicle speed, the actualvehicle speed is compared with a second predetermined vehicle speed V₂set for brake actuation which is higher than the first predeterminedvehicle speed V₁. In this case, the direct clutch valve DC is kept beingswitched ON when the actual vehicle speed is higher than the secondpredetermined vehicle speed V₂ ; whereas the direct clutch valve DC isswitched OFF when the former speed is lower than the latter speed.

If the direct clutch valve DC is controlled in the above way, when thebrakes are applied under a running condition with the direct clutchvalve DC being switched ON, the reference engine speed is lowered sincethe depression of the accelerator pedal is released to depress the brakepedal. The vehicle speed is reduced along the lines L₈ and L₄ on whichthe speed reduction ratio is minimum in FIG. 10 with the direct clutchvalve DC being switched ON. When the vehicle speed attains to the secondvehicle speed V₂, a driving signal is fed from a controller 100 to thesolenoid valves 151 and 152, and the spool member 54 of the second servovalve 50 is descended to switch the direct clutch DC OFF.

When the depression of the accelerator pedal is lessened to reduce thevehicle speed without applying the brakes, the throttle opening isreduced to lower the reference engine speed, and therefore the vehiclespeed is reduced along the lines L₈ and L₄ on which the speed reductionratio is minimum. However, when the vehicle speed reaches the firstvehicle speed V₁, which is lower than the second vehicle speed V₂, thedirect clutch valve DC is switched OFF. When the vehicle speed hasreached to a predetermined value (the vehicle speed at a point c in thedrawing in FIG. 10), the clutch valve CL is opened to interrupt thepower transmission from the engine to the wheels. Accordingly, thevehicle speed is reduced with the rotation of the engine being kept in aidling state to prevent the engine from stalling.

The ON/OFF control of the direct clutch valve is controlled by decidingwhether or not the vehicle speed is less than the predetermined vehiclespeeds V₁ and V₂ in the above case. The vehicle speed is proportional tothe engine speed because the speed reduction ratio remains minimum.Accordingly, the ON/OFF control of the direct clutch valve can beconducted based on the engine speed instead of the vehicle speed.

In the above-described control, the direct clutch valve is switched fromON to OFF at a higher speed when the vehicle is decelerated with thebrakes being applied, than when it is decelerated without braking.According, the direct clutch valve is switched OFF at an earlier stageif the brakes are applied, so that the rapid drop of the engine speed ataggressive braking which may cause engine stall can be avoided. Inaddition, when the vehicle is decelerated without braking, the vehiclespeed for switching the direct clutch valve OFF can be set at a lowlevel, whereby the engine speed can be lowered early at the decelerationof the vehicle to decrease the fuel consumption and the vibration levelduring traveling.

Although in the above embodiments, the device for controlling the angleof the motor trunnion plate is connected to the direct clutch device bya link mechanism, a link mechanism of another structure may be used orthe direct clutch device may, of course, be controlled independently.

Also, the above embodiments are described about a continuously variablespeed transmission in which the input shaft 1 is connected to the pumpcylinder 60 and the supporting portion 70a of the pump swash plate 63 iscoupled with the motor cylinder 70 which is arranged on the outerperiphery of the pump cylinder 60. However, the present invention is notlimited to the direct clutch device in the above continuously variablespeed transmission. For example, a clutch device in the presentinvention may be used for a continuously variable speed transmission inwhich a pump cylinder and a motor cylinder are horizontally arranged. Inaddition the direct clutch device may be used for another typecontinuously variable speed transmission wherein; the angle of the swashplate of the pump is variable, the motor is of a constant displacementtype, the input shaft is connected to the pump cylinder, the pumpcylinder is connected to the supporting member of the motor swash plate,and the motor cylinder is connected to the output shaft.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A hydraulic continuously variable speed transmission with a direct clutch valve comprising:a hydraulic pump connected to an engine in a vehicle; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting said hydraulic pump and said hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; and a direct clutch valve controlling device for controlling operations of said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with the actuation of said speed reduction ratio control actuator; wherein, said direct clutch valve controlling device maintains direct connecting state in which said closed circuit is being blocked by said direct clutch valve when an actual engine speed is higher than a direct clutch disconnecting reference engine speed set in accordance with a parameter indicating driver's intention of acceleration, and then said direct clutch valve control device releases the blocking of the closed circuit by said direct clutch valve when a drop of the actual engine speed from the direct clutch disconnecting reference engine speed exceeds a predetermined amount corresponding to a vehicle speed of said vehicle.
 2. A hydraulic continuously variable speed transmission as defined in claim 1, wherein said parameter representing driver's intention of acceleration is determined based on an accelerator opening.
 3. A hydraulic continuously variable speed transmission with a direct clutch valve comprising:a hydraulic pump connected to an engine in a vehicle; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting said hydraulic pump and said hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; and a direct clutch valve controlling device for controlling operations of said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with the actuation of said speed reduction ratio control actuator; wherein, said direct clutch valve controlling device maintains direct connecting state in which said closed circuit is being blocked by said direct clutch valve when an actual engine speed is higher than a direct clutch disconnecting reference engine speed set in accordance with a parameter indicating driver's intention of acceleration, and then said direct clutch valve control device releases the blocking of the closed circuit by said direct clutch valve when a drop of the actual engine speed from the direct clutch disconnecting reference engine speed exceeds a predetermined amount corresponding to a vehicle speed of said vehicle; wherein said hydraulic pump is a constant displacement swash plate type axial plunger hydraulic pump, and said hydraulic motor being a variable displacement swash plate type axial plunger motor; a cylinder member of said hydraulic pump being connected to said engine and a motor cylinder member of said hydraulic motor being connected to said output shaft; and a swash plate of said hydraulic pump being supported by a portion of said cylinder member of said hydraulic motor.
 4. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine in a vehicle; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with actuation of the speed reduction ratio control actuator; and accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit.
 5. A hydraulic continuously variable speed transmission as defined in claim 4, further comprising vehicle speed detection means for detecting a vehicle speed of said vehicle,wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the vehicle speed detected by said vehicle speed detection means is less than a predetermined vehicle speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit.
 6. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine in a vehicle; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with actuation of the speed reduction ratio control actuator; and accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; further comprising vehicle speed detection means for detecting a vehicle speed of said vehicle, wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the vehicle speed detected by said vehicle speed detection means is less than a predetermined vehicle speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; wherein brake actuation detection means for detecting actuation of vehicle brakes is provided, and said predetermined speed is set higher in a case where the brake actuation detection means detects the actuation of the brakes than in a case where the brakes are unactuated.
 7. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine in a vehicle; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with actuation of the speed reduction ratio control actuator; and accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; wherein said hydraulic pump is a constant displacement swash plate type axial plunger hydraulic pump and said hydraulic motor is a variable displacement swash plate type axial plunger pump; a cylinder member of said hydraulic pump being connected to said engine, a cylinder member of said hydraulic motor being connected to said output shaft, and a swash plate of said hydraulic pump being supported by said cylinder member of said hydraulic motor.
 8. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with the actuation of the speed reduction ratio control actuator; accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; and engine speed detection means for detecting engine speed; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the engine speed detected by said engine speed detection means is less than a predetermined engine speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit.
 9. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with the actuation of the speed reduction ratio control actuator; accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; and engine speed detection means for detecting engine speed; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the engine speed detected by said engine speed detection means is less than a predetermined engine speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; wherein brake actuation detection means for detecting actuation of vehicle brakes is provided, and said predetermined speed is set higher in a case where the brake actuation detection means detects the actuation of the brakes than in a case where the brakes are unactuated.
 10. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with the actuation of the speed reduction ratio control actuator; accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; and engine speed detection means for detecting engine speed; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the engine speed detected by said engine speed detection means is less than a predetermined engine speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; wherein said hydraulic pump is a constant displacement swash plate type axial plunger hydraulic pump and said hydraulic motor is a variable displacement swash plate type axial plunger pump; a cylinder member of said hydraulic pump being connected to said engine, a cylinder member of said hydraulic motor being connected to said output shaft; and a swash plate of said hydraulic pump being supported by a portion of said cylinder member of said hydraulic motor.
 11. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine in a vehicle; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with actuation of the speed reduction ratio control actuator; and accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; further comprising vehicle speed detection means for detecting a vehicle speed of said vehicle, wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the vehicle speed detected by said vehicle speed detection means is less than a predetermined vehicle speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; wherein said hydraulic pump is a constant displacement swash plate type axial plunger hydraulic pump and said hydraulic motor is a variable displacement swash plate type axial plunger pump; a cylinder member of said hydraulic pump being connected to said engine, a cylinder member of said hydraulic motor being connected to said output shaft, and a swash plate of said hydraulic pump being supported by said cylinder member of said hydraulic motor.
 12. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine in a vehicle; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with actuation of the speed reduction ratio control actuator; and accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; further comprising vehicle speed detection means for detecting a vehicle speed of said vehicle, wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the vehicle speed detected by said vehicle speed detection means is less than a predetermined vehicle speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; wherein brake actuation detection means for detecting actuation of vehicle brakes is provided, and said predetermined speed is set higher in a case where the brake actuation detection means detects the actuation of the brakes than in a case where the brakes are unactuated; wherein said hydraulic pump is a constant displacement swash plate type axial plunger hydraulic pump and said hydraulic motor is a variable displacement swash plate type axial plunger pump; a cylinder member of said hydraulic pump being connected to said engine, a cylinder member of said hydraulic motor being connected to said output shaft, and a swash plate of said hydraulic pump being supported by said cylinder member of said hydraulic motor.
 13. A hydraulic continuously variable speed transmission comprising:a hydraulic pump connected to an engine; a hydraulic motor connected to an output shaft; a hydraulic closed circuit for hydraulically connecting the hydraulic pump and the hydraulic motor; a direct clutch valve placed in said closed circuit to block said closed circuit; a speed reduction ratio control actuator for varying displacements of at least one of said hydraulic pump and said hydraulic motor to control speed reduction ratio; a direct clutch valve controlling device for controlling said direct clutch valve to block the closed circuit when the speed reduction ratio becomes substantially "1" in accordance with the actuation of the speed reduction ratio control actuator; accelerator opening detection means for detecting an accelerator opening which indicates driver's intention of acceleration; and engine speed detection means for detecting engine speed; wherein, said direct clutch valve controlling device releases the blocking of the closed circuit by said direct clutch valve when the engine speed detected by said engine speed detection means is less than a predetermined engine speed and also when the accelerator opening detected by said accelerator opening detection means is substantially fully closed during running with said direct clutch valve blocking the closed circuit; wherein brake actuation detection means for detecting actuation of vehicle brakes is provided, and said predetermined speed is set higher in a case where the brake actuation detection means detects the actuation of the brakes than in a case where the brakes are unactuated; wherein said hydraulic pump is a constant displacement swash plate type axial plunger hydraulic pump and said hydraulic motor is a variable displacement swash plate type axial plunger pump; a cylinder member of said hydraulic pump being connected to said engine, a cylinder member of said hydraulic motor being connected to said output shaft; and a swash plate of said hydraulic pump being supported by a portion of said cylinder member of said hydraulic motor. 